Handle vmservice messages while at breakpoint.

runtime/bin/vmservice/client/lib/src/observatory_elements/message_viewer.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library message_viewer_element;
 
 import 'package:polymer/polymer.dart';
 import 'observatory_element.dart';
 
 @CustomTag('message-viewer')
 class MessageViewerElement extends ObservatoryElement {
   Map _message;
   @published Map get message => _message;
 
   @published set message(Map m) {
     _message = m;
     notifyPropertyChange(#messageType, "", messageType);
     notifyPropertyChange(#members, [], members);
   }
 
   MessageViewerElement.created() : super.created();
 
   String get messageType {
     if (message == null || message['type'] == null) {
       return 'Error';
     }
+    print("Received message of type '${message['type']}' :\n$message");
     return message['type'];
   }
 
   List<Map> get members {
     if (message == null || message['members'] == null) {
       return [];
     }
     return message['members'];
   }
 }